The present invention generally relates to an apparatus for ventilation systems which have means for the transfer of sensible heat and/or water moisture between exhaust air (taken from inside a building) and exterior fresh air (drawn into the building). Such an apparatus may, for example, have means for the transfer of sensible heat and/or water moisture from warm exhaust air to cooler exterior fresh air, the systems using warm interior air as defrost air for defrosting the systems during cool weather.
The present invention, in one particular aspect, relates to an apparatus for ventilation systems which have at least one rotary heat exchanger wheel for the transfer of heat (and/or water moisture) from warm exhaust air (taken from inside a building) to cooler exterior fresh air (drawn into the building).
The present invention, in another particular aspect, relates to a ventilation apparatus for ventilation systems having an exchanger body which may comprise one or more heat exchanger elements of the same or different type e.g. one or more rotary and/or one or more stationary (i.e. non-rotary) exchanger elements or cores.
The present invention, in a further particular aspect, relates to a ventilation apparatus provided with means for balancing fresh air and exhaust air flow through the operating ventilation apparatus; a method for balancing airflow though the apparatus is also provided.
Sensible heat and/or water moisture recovery ventilation systems are known which function to draw fresh exterior air into a building and to exhaust stale interior air to the outside. The systems are provided with appropriate ducting, channels and the like which define a fresh air path and an exhaust air path whereby interior air of a building may be exchanged with exterior ambient air; during ventilation the air in one path is not normally allowed to mix with the air in the other path.
A sensible heat and/or water moisture recovery ventilator device or apparatus, which may form part of a ventilation system, in addition to being provided with corresponding air paths may also be provided with one or more exchanger elements or cores, e.g. one or more rotary and/or stationary (i.e. non-rotary) exchanger elements or cores. Heat recovery ventilation devices may also have a housing or cabinet; such enclosures may for example be of sheet metal construction (e.g. the top, bottom, side walls and any door, etc. may be made from panels of sheet metal). The heat exchanging core(s), as well as other elements of the device such as, for example, channels or ducts which define air paths, filtration means,insulation and if desired one or more fans for moving air through the fresh air and exhaust air paths may be disposed in the enclosure. Such ventilation devices may be disposed on the outside of or within a building such as a house, commercial building or the like; appropriate insulation may be provided around any duct work needed to connect the device to the fresh air source and the interior air of the building.
A stationary heat exchanger element(s) may, for example, take the form of the (air-to-air) heat exchanger element as shown in U.S. Pat. No. 5,002,118 the contents of which are incorporated herein by reference. Thus, the heat exchanger element(s) may have the form of a rectangular parallepiped and may define a pair of air paths which are disposed at right angles to each other; these exchanger element(s) may be disposed such that the air paths are diagonally oriented so that they are self draining (i.e. with respect to any condensed or unfrozen water).
Another known type of exchanger element is the rotary thermal and/or desiccant wheel; such (air-to-air) exchanger wheels may have an air permeable heat exchange matrix which provides passageways therethrough through which an air stream may flow. The exchanger matrix may, for example, comprise a plurality of parallel flow channels (see for example U.S. Pat. No. 4,769,053) or even a random matrix media (see for example U.S. Pat. No. 5,238,052). Such exchangers may be configured and disposed such that as they rotate they may transfer a member of the group comprising i) sensible heat and ii) sensible heat and latent heat, between two or more streams of air through which the exchangers rotationally pass through. Such rotary heat exchangers may be disposed in a housing which is suitably baffled such that a rotating exchanger wheel may pass through the fresh air and exhaust air streams with minimal intermixing thereof (i.e. for air-to-air transfer of latent/sensible heat).
Thus, for example, as a suitably configured rotary transfer core slowly rotates between outgoing and ingoing air the higher temperature airstream can give up sensible energy to the core which energy may thereafter be given up by the core to the lower temperature air stream; please see, for example, U.S. Pat. No. 3,844,737. Alternatively, a suitably configured rotary core may capture and release latent energy in the form of water moisture i.e. the core may transfer water vapour or moisture from one air stream to another air stream; please see, for example, U.S. Pat. Nos. 3,800,515, 3,844,737, 4,225,171, and 4,875,520. A rotary energy transfer core or wheel may of course transfer both sensible and latent heat between fresh air and exhaust air; please see, for example, Canadian patent No. 1,285,931, and U.S. Pat. Nos. 4,769,053, 4,172,164, 4,093,435, and 5,238,052. The entire contents of the above mentioned patents are herein incorporated by reference.
During the winter season, the outside air is not only cool but it is also relatively dry. Accordingly, if cool dry outside air is brought into a building and the warm moist interior air of the building is merely exhausted to the outside, the air in the building may as a consequence become uncomfortably dry. A relatively comfortable level of humidity may be maintained in a building by inter alia exploiting an above mentioned desiccant type thermal wheel for transferring water from the stale outgoing air to the relatively dry fresh incoming air. During winter these types of heat exchangers may transfer up to 80% of the moisture contained in the exhaust air to the fresh supply air. Advantageously a rotary exchanger wheel may transfer both sensible and latent heat between fresh air and exhaust air; in this case the exhaust air stream as it is cooled may also be dried whereas the incoming fresh air may be warmed as well as humidified. However, a problem with such heat recovery ventilation equipment having a desiccant type heat exchanger wheel, is the production of frost or ice in the air permeable beat exchange matrix of the thermal wheel.
During especially cold weather such as −10° C. or lower (e.g. −25° C. or lower), prior to expelling the relatively warm exhaust air, the equipment provides for the transfer of latent heat from the relatively warm moist exhaust air to the relatively cool dry (fresh) outside air by the use of a suitable desiccant type heat exchange wheel. However, the cooling of the relatively moist interior air by the cold exterior air can result in the formation of ice (crystals). An uncontrolled buildup of ice within the matrix of a rotary exchanger wheel can result in decreased heat transfer, and even outright blockage not only of the exhaust air path but the (cold) fresh air path as well. Accordingly a means of periodically defrosting such a system is advantageous in order to maintain the system's efficiency.
A defrost mechanism has been suggested wherein the fresh air intake is periodically blocked off by a damper and warm interior air is injected, via a separate defrost air conduit, into the fresh air inlet side of the fresh air path of the ventilation apparatus. However, during the defrost cycle, the stale inside air is still exhausted to the outside via the exhaust air path; this is disadvantageous since by blocking only the fresh air inlet and continuing to exhaust interior air to the outside, a negative air pressure can be built up in the interior of a building relative to the exterior atmosphere. Such a negative pressure may induce uncontrolled entry of air through any cracks and crannies in the structure of the building; the negative pressure may, in particular, produce a backdraft effect, for oil and gas type heating systems, whereby exterior air may be pulled into the chimney leading to the accumulation of gaseous combustion products in the building.
An alternate system has been suggested wherein both the fresh air inlet and exhaust air outlet are both blocked off such that warm interior air is circulated through the fresh air side of the heat exchanger element as well as through the exhaust air side of the heat exchanger element and is sent back into the building; see for example U.S. Pat. No. 5,193,610 the entire contents of which are incorporated herein by reference.
It is desirable that the defrosting time period be as short as possible and in particular not be greater than 25% of the time period during which a ventilation apparatus is in the ventilation configuration (e.g. if the ventilation time period is 32 minutes then desirably the defrosting time period should not be greater than about 8 minutes). However, it has been found that adapting the technique shown in U.S. Pat. No. 5,193,610 to a rotating heat exchanger wheel by directing interior defrost air through the defrost side of the wheel and then returning the air to the building by passing it through the fresh air side of the wheel while the wheel is rotating at its usual operational or ventilation cycle rotational speed (e.g. a usual ventilation speed of 15 rpm) does not produce the desired degree or efficiency of defrosting; in this case, heat which is initially taken up by the wheel from the warm interior building air is transferred back to the interior air prior to the air being recycled to the interior of the building such that the full heat of the interior air is not utilized for defrosting. If the usual rotational speed mentioned above is maintained, defrosting occurs over a relatively significant time period (e.g. a defrost time of 18 minutes or more) relative to the ventilation time period (e.g. a ventilation time of 32 minutes) during which the apparatus is operating; i.e. the defrosting period may represent more than 25% of the ventilation operating time which means that this defrosting technique is relatively inefficient keeping in mind that during such defrosting, the system is not carrying out its primary function, namely the ventilation of a room or building.
Another problem with respect to ventilation systems comprising a heat exchanger element or core relates to the installation of an exchanger device in a building such as for example a house or other type of building. In order for the system to operate efficiently and effectively the outgoing exhaust air flow preferably at least substantially equals the incoming fresh air flow; i.e. the exhaust and fresh air flows are preferably balanced so as to minimize or eliminate under-pressure or over-pressure in the house relative to the outside atmospheric pressure; a certain degree of overpressure may, however, be tolerated.
Presently, such ventilation systems are balanced by means of balancing dampers and removable flowmeters such as, for example, a pitot tube type flow measuring device comprising a manometer to measure pressure difference; these elements must usually be installed by the balancing technician at appropriate places in the duct work connected to the ventilation device.
Thus, for example, one removable flowmeter element may be installed in a duct on the exhaust air inlet side of the device and another flowmeter element may be installed in a duct on the fresh air outlet side of the ventilator device. However, the removable flowmeter detector elements must be temporarily installed between straight lengths of duct of relatively sufficient length so as to be localized in a relatively stable airflow (steady state condition) and thus minimizes erroneous or misleading readings due to turbulence as may be encountered about an elbow or bend element of a duct.
The exhaust and fresh air flows may be initially measured by placing the balancing dampers parallel to the air flow so as to present a minimum resistance to air flow. The fresh air and exhaust air flow rates may then he determined using the respective flowmeters. A fresh air damper may in this case be adjusted so as to reduce the fresh air flow out of the ventilator to be equal to or be up to about +5% of the exhaust air input to the ventilator, i.e. as the damper is turned, so as to present a larger surface area transverse to the direction of the air flow, the flowmeter is monitored and the adjustment stopped once the flowmeter indicates a flow rate more or less equal to that of the exhaust air flowing into the ventilator as initially determined.
The exhaust air flow rate into the ventilator may then be remeasured and, if necessary, (i.e. if the exhaust flow is higher than the fresh air input flow), the exhaust air damper may be adjusted (i.e. turned into the air flow) so as to reduce the exhaust air flow input into the ventilator to more or less equal the adjusted fresh air flow out of the ventilator. For example, the exhaust air flow may be adjusted so as to be somewhat smaller than the fresh air flow so as to provide a slight overpressure in the building, i.e. so as, for example, to inhibit uncontrolled entry of fresh air through other parts of the building. Thereafter at least the flowmeters must be removed and replaced by the balancing technician with appropriate duct portions. This procedure as may be appreciated is time consuming and may take up to an hour or more of a technician's time.
It would therefore be advantageous to have a rotating wheel heat exchanger system which can use interior air as defrost air so as to diminish or avoid the creation of a negative air pressure in the building.
It would also be advantageous to have a defrostable ventilation apparatus which is of simple construction.
It would be advantageous to be able to operate a ventilation apparatus during periods of cool exterior temperature for an extended period of time before having to defrost it. It would in particular be advantageous to have a rotating wheel heat exchanger type system which can operate for extended periods of time during periods of cool exterior temperatures before having to be defrosted.
It would in another aspect be advantageous to have an alternate method and means for balancing input and output airflow through a heat exchanger device or system.
It would in particular be advantageous to have a means of relatively simple construction for balancing input and output airflow through a heat exchanger device or system.